Balloon angioplasty and mechanical atherectomy are the two principal endovascular medical procedures which have been developed for management of lesions in the coronary, visceral, and peripheral artery trees of patients having medical conditions judged suitable for such procedures or, alternatively, of patients having medical conditions judged unsuitable for surgical artery-bypass procedures.
Briefly, in the balloon angioplasty procedure, a substantially uninflated balloon at or near the tip of a catheter system is advanced inside an artery toward a predetermined (for example, by prior radiological procedures) location within the artery, where blood flow has been restricted or curtailed by build up of plaque. Upon positioning the tip of the catheter system at the location of the lesion (depending on the medical characteristics of the lesion, a lesion is also referred to either as a stenosis or as an occlusion), the balloon is inflated to create radial (and possibly some axial) forces, directed outwardly against the lesion, thereby displacing the plaque constituting the lesion by redistributing the plaque material over a now radially expanded arterial wall (also referred to as a dilated arterial adventitia). Hence, plaque displacement by the inflated balloon results in an enlarged open channel (also referred to as the lumen) within the artery at the location of balloon intervention, thus ensuring, at least in principle, improved blood flow through this previously restricted artery at that location.
In contrast to balloon angioplasty, atherectomy procedures are aimed at cutting, grinding, ablating or vaporizing plaque or other material from lesions within arteries, veins or vascular shunts. Plaque ablation may occur predominantly by localized endovascular application of ultrasonic energy, while plaque vaporization is likely the predominant process in localized endovascular application of optical energy from a laser source.
A common feature of present mechanical cutting or grinding atherectomy devices is the fixed dimension of a selected cutter or grinder means, suitably deposed at or near the distal end of a generally coaxially arranged atherectomy system. Means for advancing or retracting the cutting or grinding devices and associated rotational drive shafts, guide wires (when used), and outermost catheter tubes to or from the predetermined location of a lesion inside an artery are provided at the outside of the patient's body, as are rotational cutter drive means (for example, a motor or a turbine driven by compressed air) and means for introducing, as into the coaxial atherectomy system, certain fluids and/or means to extract (usually by controlled suction) lesion debris cut or ground at the location of the lesion within the artery under treatment. For purposes of clarity, such coaxially arranged advancing and retracting means, rotational drive means, fluid introduction and debris-extraction means will be collectively called "coaxial supply." The terms artery, vein, vascular shunt comprehend different types of vascular channels wherein the invention is useful; i.e. the system of the invention is useful in endovascular surgery in vascular channels where one type of vascular channel is mentioned (e.g. an artery) it will be appreciated that the invention is not restricted for use in connection with only such a channel.
An overview, as well as a more detailed description of present mechanical atherectomy systems and respective procedures and clinical results can be found in Endovascular Surgery; second edition; Samuel S. Ahn and Wesley S. Moore, editors; published by Saunders, Philadelphia, Pa; 1992, particularly chapters 28-34, pages 263-319.
While each of the present mechanical atherectomy systems offers certain procedural advantages for specific classes of lesions (for example, relatively hard, calcified plaque or relatively soft, partially compliant or rubbery plaque), the fixed dimension of the cutter associated with each of the present atherectomy systems necessitates, in some procedures, several sequential groups of steps (insertion, cutting of plaque, and complete removal of the system from the artery under treatment), starting with the smallest-dimension cutter device and progressing through larger dimension cutter devices with each respectively associated coaxial supply. This sequential procedure is time-consuming and can result in attendant medical complications.
The invention avoids such procedures and provides a single, sequentially and selectively expandable cutter surface in a mechanical atherectomy system to facilitate maximum plaque removal at each of a potential plurality of plaque locations within one and the same artery or vein with a single endovascular insertion into that artery or vein of the cutter and its associated coaxial supply.
Present mechanical atherectomy systems also use a mechanically rigid, i.e., non-compliant cutter. Rigidity or non-compliance of a cutter may be acceptable in instances where the lesion within the artery or vein is firstly located in a relatively straight, i.e., uncurved, section of the artery or vein, and is secondly composed of essentially similar material, for example, substantially calcified deposits or substantially soft or compliant deposits. Frequently, a plurality of different lesions (different in composition and different in the degree of lesion fill factor, i.e, the extent to which a lesion occupies internal arterial volume) are found along an artery, with some lesions located in relatively straight sections of the artery and other lesions located in relatively curved sections. Rigid, non-compliant cutters of present mechanical atherectomy systems generally are not suited to effectively recanaliz an artery having such a plurality of different lesions located in said various sections of an artery. In fact, present rigid cutters can perforate through the wall of an artery or vein because they do not possess adequate self centering capability, a feature particularly important in curved section of an artery or vein.
It is a feature of the invention to provide a compliant cutter surface as part of a mechanical atherectomy system which is advantageous for lesion removal from sections of arteries or veins of straight or curved shape.
As pointed out in several chapters in the above-referenced publication, Endovascular Surgery, clinical outcomes of endovascular mechanical atherectomy have been improved sometimes when balloon angioplasty was performed subsequent to mechanical atherectomy, so as to redistribute any remaining lesion material somewhat uniformly along the inside of the arterial wall, and hence, to affect a wider and smoother lumen than could be obtained with either procedure alone.
Features of the invention are: (a) to provide a generally ellipsoidally-shaped compliant cutter which offers improved self-centering during endovascular cutting procedures; (b) to provide a non cutting, gentle balloon-like capability on at least a portion of the surface area of a selectively expandable compliant cutter, such that at least a partial smoothing of remaining lesion material may be affected; (c)to provide on at least first portions of the compliant cutter surface, a plurality of cutter elements, and to provide on at least second portions of the compliant cutter surface a non-cutting, gentle balloon like smoothing capability; (d)to enable the physician to select the location, frequency, distribution, size and shape of a plurality of cutter elements on at least portions of the surface of a compliant cutter, which may be on first portions of the surface; second portion of the surface being expandable to provide a non-cutting balloon-like smoothing capability; and (e) to enable the physician to select a sequentially and selectively expandable cutter surface, the degree of expansion of which is selectable by the physician.